8252043: Move inner class metaspace cleaning out of safepoint cleanup tasks

Clean up inner metaspaces from ServiceThread if cleanup is needed for concurrent GCs.

Reviewed-by: eosterlund, pchilanomate

src/hotspot/share/gc/parallel/psParallelCompact.cpp

@@ -1056,7 +1056,7 @@ void PSParallelCompact::post_compact()
   }
 
   // Delete metaspaces for unloaded class loaders and clean up loader_data graph
-  ClassLoaderDataGraph::purge();
+  ClassLoaderDataGraph::purge(/*at_safepoint*/true);
   MetaspaceUtils::verify_metrics();
 
   heap->prune_scavengable_nmethods();